A man who took his ex-girlfriend's pregnancy test for a joke discovered he had testicular cancer after his positive result was flagged up online.

The man's friend had posted a comic drawing on the Reddit website showing how surprised he was at finding he was an expectant male.

But an alert reader suggested there might be another, serious reason for the reading.

"You may have testicular cancer. Get to an oncologist, tell them you took a pregnancy test and it came out positive," the person wrote.

The joker took the advice and went to his doctor, who found a small tumour on his right testicle.

His friend has since posted an update on what happened.

He said: "To be honest with everyone, I assumed it was nothing, considering a pregnancy test finding cancer seemed a bit odd.

"But I guess there is a hormone the test picks up that the tumour produces, and that is why the test said he was pregnant."

The friend added: "So both of us want to say, 'Thank you.' And, in all seriousness, if you are male, check yourself for testicular cancer regularly. If you're a girl, test yourself for breast cancer regularly."

The connection with the pregnancy test and the finding of testicular cancer is that some testicular cancers produce the same hormone - beta hCG - that is tested for in pregnancy kits.